The invention relates to validation of a calling subscriber in a telecommunications system in which at least some of the subscribers also have access to the network of another operator through the network of their operator (i.e., through the network to which the subscribers themselves are attached).
With the liberalization of telecommunications legislation, new tele-operators have emerged in many countries who start competing with the old operators for customers. In such an environment, subscribers attached to the network of a given operator can make a call through the network of another operator by using a prefix identifying the desired-operator in front of the dialled number. From the point of view of said second operator, such subscribers have indirect access to the network of said operator. Such subscribers will be termed subscribers of indirect access in the following.
In many countries, however, operators are not obliged to carry out charging if a subscriber attached to their network desires to make a call through the network of another operator. In such cases, said second operator must carry out charging independently. Then a contract must be concluded between the customer (subscriber) and operator to the effect that the subscriber has access to the network of said operator even though the subscriber is attached to the network of another operator. In the connection setup phase, a check is made on the basis of which it is recognized whether said subscriber is entitled to access to the network. This operation is termed calling party validation.
FIG. 1 illustrates the different steps in connection setup when calling party validation is performed on the basis of which he is granted access to the network to which his terminal is not directly attached. The different steps are denoted with circled numbers 1 . . . 5. In the example shown in the figure, the calling subscriber SB1 is attached to the network of operator A, and said subscriber desires to place a call through the network of operator B.
When subscriber SB1 initiates a call that he desires to be established through the network of a given operator, he dials a prefix (XYZ) indicating the desired operator, in this exemplary case operator B, in front of the telephone number. This prefix and the number of the called subscriber, among other data, are sent in a standard initiation message to the subscriber""s terminal exchange (step 1). At the terminal exchange SW1, a digit analysis is performed on the received number, in which connection it is found on the basis of the prefix itself that the call is intended to the network of operator B (step 2). The call attempt is thus routed to an inter-operator link IOL (step 3). The exchange SW2 located in the network of operator B, at the opposite end of the link IOL, comprises a database DB by means of which calling party validation is performed. This is effected by comparing the number of the calling subscriber (A number) with the valid numbers in the database (step 4). The validation process can be triggered at the exchange SW2 for example on the basis of the dialled prefix or on the basis of the incoming circuit group.
If the subscriber is found to be a valid subscriber, the call setup is continued in the normal way on the basis of the data of the call attempt (step 5). If, on the other hand, the number of the calling subscriber is not found from among the valid subscribers, the call is routed to a service from which additional information on the missing authorization is obtained, for example to a voice announcement or to a specific service number.
Seen on the network level, a calling subscriber validation of the above kind has been implemented either by the conventional technique as an exchange-based solution (as presented above) or as a solution based on an intelligent network.
FIG. 2 illustrates the above exchange-based solution on a network level. Calling subscriber validation is performed at each exchange (SW1xe2x80x2, SW3xe2x80x2) from which there is an interoperator link (IOL) to the network of the neighbouring operator to which the subscribers of indirect access are attached. One drawback of this solution is that the maintenance and commissioning of the database is difficult, as the database must generally be located in several different exchanges (usually there are several interoperator links).
If, on the other hand, it is attempted to avoid the problem by performing the validation at one exchange only, transmission capacity is wasted, as in that case all calls are routed through the same validating exchange. At the same time, extra unwanted speech routes are created in the network. Neither is it worth-while to distribute the database in such a way that each validating exchange would only have information on some of the subscribers with indirect access, since in that case extra logic for routing calls through the correct exchange in each case should be created in the network.
These problems can be evaded by using the above-stated solution based on an intelligent network that has been illustrated in FIG. 3. In this case, the validation of the calling subscriber is performed in such a way that all exchanges from which there is an interoperator link to the exchange of a neighbouring operator send a validation enquiry to the service control point SCP at which the database (DB) of the valid subscribers is located. Depending on the response given by the SCP node, the call is routed either forward to the called number or to a service at which an announcement on missing authorization is given. Thus, the call setup is xe2x80x9cfrozenxe2x80x9d at the exchange on the border of the network for the duration of the enquiry made to the SCP node and the call setup is continued with after a response has been obtained, to a destination dependent on the content of the response.
In practice, however, the technique based on an intelligent network is costly, for which reason implementation of calling subscriber validation is clearly a more expensive alternative than that using the conventional exchange-based technique. Since the check is a very simple operation and since the number of checks to be performed is high, it is not reasonable, either, to load the service control point too much by operations that could easily be realized using an exchange-based technique as well. Intelligent network resources should therefore preferably be reserved solely for more complex and demanding services.
It is an object of the invention to eliminate the drawbacks described above and to provide a method wherewith the advantages of the above prior art methods can be combined.
This object is achieved with a solution as defined in the independent claim.
The idea of the invention is firstly to maintain in a network, by using the conventional exchange-based technique, a validating node that is in common use by several exchanges on the border of the network wherefrom there is a link to an exchange of the neighbouring operator. In the preferred embodiment, the network of the operator only has one validating node. The idea is further to carry out the connection setup phase in such a way that the connection is established from said exchanges on the border of the network up to this predetermined validating node, but if the validation performed in the latter indicates that the subscriber is entited to access to the network, transmission capacity already allocated is released backwards for at least one link span. The release is carried out at least each time the called subscriber is not beyond the validating exchange. The release is preferably performed up to the exchange on the border of the network wherefrom there is an interoperator link to the network of the operator of the subscriber. This exchange performs redirecting of the call to the desired destination, and hence the speech path is not usually switched through the validating node. In one embodiment of the invention, the validating exchange does not even attend to call switching but only serves as a validity-checking node.
When the method of the invention is used, calling subscriber validation can be implemented economically, as the solution is founded on a conventional and inexpensive exchange-based technique. Since the established connection is released at least one link span backwards, no transmission capacity is wasted and no undesired extra speech paths are created in the network. Since, moreover, the validation is centralized, the commissioning and maintenance of the this function is as simple as possible.